Portable back-up battery pack



FIG. 1 is a rear, right, top perspective view of a portable back-up battery pack;

FIG. 2 is a front, left, bottom perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is top view thereof; and,

FIG. 8 is a bottom view thereof.

The broken lines in the drawings illustrate elements of the portable back-up battery pack which form no part of the claimed design. 

CLAIM The ornamental design for a portable back-up battery pack, as shown and described. 